Electric signaling



Dec. 5, 1933. GERTH 1,938,379

ELECTRIC SIGNALING Filed Feb. 25. 1931 U 5 HH'H I M IHVFIYTOR /iz Geri/1 IUTOIPNEY Patented Dec. 5, 1933 ELECTRIC SIGNALING Felix Gerth, Berlin-Tempelhof, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin- Tempelhof, Germany Application February 25, 1931, Serial No, 518,081, and in Germany March 3, 1930 8 Claims.

My invention relates to electric signaling and more particularly to transmission systems using alternating current of medium or high frequency as a carrier for the signals, such as telegraphic signals.

When a transmitter, for instance, a high frequency transmitter is modulated by signaling currents, the resultant current, as is well known, may be dissolved into a current of the carrier frequency and an upper and a lower band of side frequencies resulting from the signal modulation. This has the disadvantage that it limits the number of possible signaling or communication channels for a given band or range of frequencies,

such as for instance the high frequency range allocated for the communication of commercial telegraphic signals or also the eifective frequency transmission band of a cable, which, as" is well known, is limited to a certain range of frequencies above which the impedance of the cable to alternating currents becomes so high as to make practical transmission impossible.

It is an object of my invention to provide means whereby a greater number of communication channels are available for a given transmission frequency range of the transmission medium.

Accordingly, a specific object of my invention is to limit the width of the side bands of a modulated signal with a view to allowing more signals to be placed within a given frequency range without danger of mutual interference of one signal with another. 7 I

A further object ofmy invention is the provision of means in a vacuum tube transmitter,

whereby the transmitted signals are rounded off at the edges and accordingly contain a decreased number of higher harmonics, producing smaller side bands without objectionable interference with the operation of the transmitter.

These and further objects of my invention will become more apparent as the following detailed description proceeds, taken with reference'to the accompanying drawing, in which I have illustrated by way of example a transmitting circuit in which the invention has been embodied.

Figure 1 illustrates the shape of the signals or' current steps, such as telegraphic code signals as they generally appear in high frequency telegraphic transmitters with very sharp edges and fjtheir modification in accordance with the invention.

Figure 2 shows a transmitter diagram of known design comprising a master oscillator and a power oscillator including the new feature of the in- 5'Ivention.

In controlling high frequency telegraphic transmitters as stated above, I provide means whereby the signals are rounded off as much as possible, so as to decrease the width of the transmission frequency band and to allow an increased number of individual transmitters to be operated within a given limited frequency range. Signals with very sharp edges, on the other hand, contain a more 'or less large number of high har-- monies of the fundamental frequency determined by the length and the spacing intervals of the signals and the transmission speed. These high harmonics, as is well known, produce side frequencies of the carrier at a comparatively far' distance from it, thus considerably widening the width of the signal transmission band. A number of different means have already been proposed to increase the number of transmission channels, but the new method and circuit in accordance with the present invention possess a number of advantages not found in the earlier arrangements and consisting, among others, primarily in that no disturbing interference'with the remaining parts of the transmitter and its operation takes place.

According to my invention, which specifically applies to the master oscillator-power amplifier type of transmitter, a damping element is inserted in the anode lead of the power amplifier, which acts toeflfect a slow increase and decrease of the anode current when the transmitter is being keyed or periodically interrupted in accordance with the signal currents. This enables the master oscillator to readily continue to oscillate during the spacing intervals of the signals, for if the master oscillator would be controlled in a similar manner, this would result in sharply edged signals, as it is well known that the oscillations of an oscillator only set in suddenly and abruptly at a definite value of the control potential, ordinarily the grid potential of the tube. In accordance with the keying arrangement of the invention, on the other hand, a very slow and steady increase of the anode current is secured without the danger of any instability phenomena or complete cessation of the oscillations.

Referring'to Figure l of the drawing, I have shown ata two signals or current impulses, consisting, for instance, of a dot and dash combination according to the Morse code with very sharp edges, such as normally occur in radio transmitters of known design, as when the master oscillator is directly controlled. At a I have illustrated the same signal with its edges rounded off,

in accordance with the invention. 1 10 Referring to the transmitting circuit shown by Figure 2, St represents a master oscillating tube connected to an output oscillatory circuit comprised by the self inductance L1 and the capacity C1. Continuous oscillations in the latter circuit may be maintained by any one of the well-known control methods, such as by a regenerative connection from the output to the grid circuit,

through a piezo electric control arrangement and the like, which, however, has not been illustrated for the sake of clearness and as being inessential for the understanding of the present invention. An inductance coil L2 serves for coupling the master oscillator with the grid circuit of the power amplifier tube H. The grid of the power amplifier carries a negative bias supplied from a potentiometer P in connection with a battery B, which is high enough to prevent transmission-of energy from the master oscillator to the power oscillator during the spacing intervals between the signals. The power amplifier tube H operates upon the utilization circuit comprising an inductance L3 and capacity C2 associated with the antenna-earth system A, E. This circuit corresponds to the well-known separately controlled transmitter circuit, comprising a master oscillator and power amplifier.

If the key T, which is connected to the terminals of the potentiometer P, is pressed down or closed, the plate current through the power tube, on account of the change of the grid bias, will obviously rise very rapidly and produce sharp edged signals, as shown by and according to Figure 1. This is prevented in accordance with the invention by a damping element D, inserted in the supply lead for the plate current of the power tube H, which damping element is designed so as to produce a slow and gradual increase or decrease of the plate current, resulting in rounded oif signals as shown by a in accordance with Figure l. v V p This damping element, in its simplest form,

may consist of an ohmic resistance which, as is nected inductance elements and parallel shunt capacities, whereby frequencies are readily passed up to a certain limit and frequencies be-.

yond that limit are suppressed or by-passed; In the present embodiment the damping element D is designed to act as a blocking device for high frequencies beyond a certain limit, corresponding to the high harmonics which it is desired to suppress in the telegraphic signals, in order to produce a suitable rounded off signal shape and to decrease the frequency band width to a desired value. The characteristic of the damping element or filter D may be designed'in such a manner that it will be effective for a given range of operating signaling speeds by properly designing its limit frequency so that no subsequent readjusting is necessary when the signaling speed of the transmitter is changed. This is a special advantage of using a filter as a damping element.

Although I have described my invention with specific reference to the illustration and particular exemplification given in the drawing, I wish it to be understood that many modifications and variations are possible and that the invention may be embodied in many forms, all coming within the broad aspects and scope, as set forth in the appended claims.

What I claim is:

l. The combination in a radio signaling system of a space charge device having cathode, anode and control electrodes; an input circuit connected to said control electrode; an output circuit connected to said anode; a source of substantially smooth direct anode current; means for setting up signaling oscillations in said output circuit; further means for starting and stopping said oscillations in accordance with signals to be transmitted; and means connected in said anode circuit for retarding the rise and fall of the anode direct current.

2. In a signaling system as claimed in claim 1 in which said last means is comprised of a frequency responsive network connected between said source and the anode of said discharge device.

3. In a signaling system as claimed in claim 1 in which said last means consists of a low pass filter connected between said source and said discharge device.

4. In a signaling system as claimed in claim 1 in which said last means is comprised of a low pass filter consisting of series inductance and parallel condensers connected between said source and said discharge device.

5. In combination with a radiant energy transmitting system; a source of oscillating signaling current; a space discharge amplifier having cathode, anode and control electrode controlled by said source; an anode output circuit of said amplifier; a source of substantially smooth direct anode current for said amplifier; means for starting and stopping said signaling oscillations in accordance with signals to be transmitted; and means for retarding the rise and fall of the direct anode current of said discharge amplifier.

6. In a transmitting system as claimed in claim 5 in which said last means is comprised of a frequency responsive damping network connected between said source and said amplifier. I

7. In a transmitting system as claimed in claim.5 in which said last means is comprised of a low pass filter connected between said source and said discharge device.

8. In a transmitting system as claimed in claim 5 in which said last means is comprised of a low pass filter consisting of series inductance elements and parallel condensers connected between said source and said discharge device, said filter having an upper cut-off frequency to suppress harmonic frequencies of predetermined order in the anode direct signaling current variations.

FELIX GERTH. 

